Environmental scanning electron microscope (ESEM/SEM) gas injection apparatus with anode integrated with gas concentrating structure

Abstract

A gas injection system provides a local region at the sample surface that has sufficient gas concentration to be ionized by secondary electrons to neutralize charged on the sample surface. In some embodiments, a gas concentration structure concentrates the gas near the surface. An optional hole in the gas concentration structure allows the charged particle beam to impact the interior of a shrouded region. In some embodiments, an anode near the surface increases the number of ions that return to the work piece surface for charge neutralization, the anode in some embodiments being a part of the gas injection system and in some embodiments being a separate structure.

We claim as follows: 
     
       1. An apparatus for providing a gas at a work piece surface in a vacuum chamber, comprising:
 a gas concentration structure for concentrating a gas at a shrouded region of the work piece, the gas concentration structure having an aperture for passing a beam to the work piece, the shrouded region being less than an entirety of the work piece, the aperture being sufficiently small to limit a conductance of the gas through the aperture; 
 a gas concentration structure support member for supporting the gas concentration structure, the gas concentration structure support member being moveable to position the gas concentration structure to concentrate the gas near a region of interest on the work piece; and 
 a gas conduit for providing the gas to a space within the gas concentration structure, 
 wherein the gas concentration structure comprises an anode configured to:
 cause an ionization of the concentrated gas; 
 drive positive ions generated by the ionization towards the work piece surface; and 
 detect a secondary electron signal amplified by the ionization. 
 
 
     
     
       2. The apparatus of  claim 1  in which the conduit comprises a hollow within the gas concentration structure. 
     
     
       3. The apparatus of  claim 1  in which the gas concentration structure support member comprises a gas concentration structure support member drive mechanism that provides for motion along a longitudinal axis to withdraw the gas concentration structure from the work piece when not in use. 
     
     
       4. The apparatus of  claim 1  further comprising a circuit for detecting electrons impinging on the anode, the electrons comprising a detector signal. 
     
     
       5. The apparatus of  claim 1  in which a shape of the gas concentration structure comprises a portion of a cone, a portion of a sphere, or at least a portion of a cylinder. 
     
     
       6. The apparatus of  claim 1  in which at least a portion of the gas concentration structure is hollow and communicates to the gas conduit for conducting gas from the conduit toward the work piece. 
     
     
       7. A charged particle beam system, comprising:
 a source of charged particles; 
 a work piece vacuum chamber; 
 a focusing lens for focusing the charged particles from the source of charged particles onto a work piece in the work piece vacuum chamber; and 
 an apparatus in accordance with  claim 1  for providing a gas at a sample surface in the work piece vacuum chamber. 
 
     
     
       8. The charged particle beam system of  claim 7  in which the source of charged particles comprises a source of electrons. 
     
     
       9. The charged particle beam system of  claim 7  in which the shroud is adapted to be positioned above the surface of the work piece to provide a region of limited gas flow between the shroud and the surface of the work piece to maintain a higher pressure within the shroud. 
     
     
       10. The charged particle beam system of  claim 7  further comprising a sample stage having a stage diameter, a portion of the shroud adapted to be closest to the work piece having a shroud diameter corresponding to the diameter of the shrouded region of the work piece, the shroud diameter being less than half the stage diameter. 
     
     
       11. A method of operating a charged particle beam system to process a work piece in a sample vacuum chamber, comprising:
 creating a region inside the vacuum chamber between a portion of a work piece surface and a as concentration structure having a first gas concentration higher than a second gas concentration elsewhere in a sample vacuum chamber, the portion of the work piece being smaller than an entire surface of the work piece and the gas concentration structure comprising an anode; 
 directing a charged particle beam toward the work piece, the charged particle beam passing through the first gas concentration; 
 applying a voltage to the anode such that the anode attracts secondary electrons generated from an impact of the charged particle beam, the secondary electrons causing an ionization cascade in the first gas concentration; 
 neutralizing an electrical charge on a portion of the workpiece with positive ions from the ionization cascade; and 
 detecting an electron current amplified by the ionization cascade using the anode to form an image. 
 
     
     
       12. The method of  claim 11  in which the gas concentration structure comprises a shroud, the shroud having an aperture to pass the charged particle beam. 
     
     
       13. The method of  claim 11  in which neutralizing an electrical charge on a portion of the workpiece with positive ions from the ionization cascade comprises neutralizing an electrical charge on a non-conductive portion of the work piece using an ionized gas. 
     
     
       14. The method of  claim 12  in which the shroud is positioned above the portion of the work piece such that gas flow between the shroud and the work piece is sufficiently small to maintain a pressure differential of at least a factor of 10 between an inside of the shroud and the sample vacuum chamber away from the work piece. 
     
     
       15. The method of  claim 14  in which the shroud contacts the work piece. 
     
     
       16. The method of  claim 14  in which the shroud is positioned less than 0.5 mm above the work piece to limit a gas conductance from inside the shrouded area to the rest of the sample vacuum chamber. 
     
     
       17. An apparatus for providing a concentration of a gas at a work piece surface in a vacuum chamber, comprising:
 a gas concentrator comprising an anode and configured to provide a concentration of a gas at a portion of a work piece surface, the portion less than the entire work piece surface, in a vacuum chamber; and 
 a gas conduit for providing the gas to the gas concentrator, 
 wherein the anode is configured to:
 cause an ionization of the concentration of the gas; 
 drive positive ions generated by the ionization towards the work piece surface; and 
 detect a secondary electron signal amplified by the ionization. 
 
 
     
     
       18. The apparatus of  claim 17  in which the gas concentrator includes a shroud having an aperture through which to pass a charged particle beam. 
     
     
       19. The apparatus of  claim 17  in which the gas concentrator does not include a shroud. 
     
     
       20. The apparatus of  claim 1  in which the gas concentration structure comprises a gas injection needle. 
     
     
       21. The method of  claim 11  in which the gas concentration structure comprises a gas injection needle. 
     
     
       22. The apparatus of  claim 17  in which the gas concentrator comprises a gas injection needle.